BMW Engine Powered by Aluminum Piston

BMW has adopted an aluminum piston developed by Federal-Mogul for use in its M550d xDrive sedan. The piston meets the strength and thermal performance requirements of very high-power diesel engines that have been designed to reduce CO2 emissions and improve fuel economy.

These diesel engines also offer improved dynamic performance, but their power output of more than 90kW/liter is a challenge for the pistons. BMW, reportedly the first automaker to adopt the new piston, will use it for its triple-turbo 3.0-liter diesel engine, the N57D30S1, which is said to be the world's most powerful light diesel engine at a specific power output of 93kW/liter.

BMW will use a new Federal-Mogul aluminum piston (right) for the triple-turbo, 93kW/liter engine (left) in its M550d xDrive sedan. The piston is design to satisfy the high heatand strength requirements of new diesel engines.(Source: Federal-Mogul)

As we've reported before, a new generation of smaller vehicle engines (like the N57D30S1) are being designed to improve fuel economy, reduce emissions, and run much hotter than previous engines. These engines require higher-grade materials.

"By combining all our process and materials expertise, Federal-Mogul has produced an aluminum piston with the durability and the thermal characteristics that high-power diesels require," Gian Maria Olivetti, its vice president of technology and innovation for powertrain energy, said in a press release. "These advances mean that aluminum pistons can retain their leading position in diesel engines for light vehicles for some time to come."

With higher specific power outputs come not only higher temperatures, but also higher mechanical loads, which make a piston's heat dissipation and strength equally important. Federal-Mogul's new aluminum piston can operate efficiently under higher thermal and mechanical loads than previous models. They also come without the risk of problems associated with steel pistons, such as engine oil cracking and carbon deposits.

The piston's design uses the company's Durabowl process, which creates a reinforced combustion bowl rim that can withstand high thermal and mechanical loads. The process remelts the alloy around the bowl's rim to improve the aluminum's fatigue strength. A raised cooling gallery, made possible by Federal-Mogul's two-dimensional ultrasonic inspection process, improves thermal performance.

Nice story, Ann. Do you know if these pistons use cast iron cylinder liners? Going way back to the old Chevrolet Vega (does anyone remember the Vega?), engineers have tried to use aluminum. When the Vega's engine had problems, engine builders started employing the cast iron liners. In the '90s, engineers got rid of the cast iron liners and started using hypereutectic aluminum alloys for the blocks and various coatings for the inside of the cylinder, but I don't know how that came out. Are they still using the liners?

Dave, thanks for the feedback on the re-melting process. I agree, it doesn't sound intuitively obvious as a manufacturing process. Regarding the alloy, I'd like to know, too: no details on this product were given. On the company's website appears this general statement about their aluminum pistons. but whether it applies to the new diesel piston is not clear: "We offer aluminum diesel pistons made of Federal-Mogul's exclusive, high-strength B3 alloy (2006) for high-end light-vehicle diesel applications, giving a 10 percent higher fatigue resistance at 440º C to absorb extreme loads in performance engines."

Ann, do you know what kind of aluminum Federal Mogul is using for this application? I assume it is an aluminum-silicon alloy. Do you know if it is hypereutectic, eutectic, or hypoeutectic? (This is metallurgy-speak for more than 12% silicon, about 12% silicon, or less than 12% silicon).

The DuraBowl re-melting process is interesting, and, like many good ideas, seems obvious in retrospect. Doing failure analysis of aluminum pistons, I've often observed that areas which melted (in service!) are much harder and have a much finer microstructure than the surrounding area. But I'm not sure that it would have occurred to me to exploit this as a manufacturing process.

Friction stir processing is another way to achieve improved properties in the piston bowl area. I'm not sure whether anyone is doing this commercially yet, but there is a lot of interest in it. At last year's Materials Science and Technology conference, Dr. Saumyadeep Jana gave a presentation on friction stir processing of cast aluminum alloys; during the Q&A session, it was clear that just about everyone in the audience (including myself!) had pistons on their mind. I strongly suspect we'll be seeing friction stir processed pistons in the next couple years. This would be a good topic for an article.

The aluminum industry has been working on high-strength versions, including alloys such as aluminum-lithium, for some time now. For example, it's the major metal in aircraft, where it's mostly replaced steel (see my upcoming July feature article on aircraft materials). We've also covered a brake rotor prototype made of an aluminum composite:http://www.designnews.com/author.asp?section_id=1392&doc_id=239090Aluminum rotors aren't new, but this one is managing to keep up with the increasing heat requirements of today's smaller, hotter engines, not a small feat. There are some under-hood applications of plastics, including carbon composites, such as this one I wrote abouthttp://www.designnews.com/author.asp?section_id=1392&doc_id=243857but AFAIK, not yet in car engines.

Many of the new adhesives we're featuring in this slideshow are for use in automotive and other transportation applications. The rest of these new products are for a wide variety of applications including aviation, aerospace, electrical motors, electronics, industrial, and semiconductors.

A Columbia University team working on molecular-scale nano-robots with moving parts has run into wear-and-tear issues. They've become the first team to observe in detail and quantify this process, and are devising coping strategies by observing how living cells prevent aging.

Many of the new materials on display at MD&M West were developed to be strong, tough replacements for metal parts in different kinds of medical equipment: IV poles, connectors for medical devices, medical device trays, and torque-applying instruments for orthopedic surgery. Others are made for close contact with patients.

Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.